<SEC-DOCUMENT>0000018230-11-000130.txt : 20110304
<SEC-HEADER>0000018230-11-000130.hdr.sgml : 20110304
<ACCEPTANCE-DATETIME>20110304172646
ACCESSION NUMBER:		0000018230-11-000130
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20110303
FILED AS OF DATE:		20110304
DATE AS OF CHANGE:		20110304

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			OSBORN WILLIAM A
		CENTRAL INDEX KEY:			0001171797

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-00768
		FILM NUMBER:		11665795

	MAIL ADDRESS:	
		STREET 1:		100 NE ADAMS STREET
		CITY:			PEORIA
		STATE:			IL
		ZIP:			61629

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			CATERPILLAR INC
		CENTRAL INDEX KEY:			0000018230
		STANDARD INDUSTRIAL CLASSIFICATION:	CONSTRUCTION MACHINERY & EQUIP [3531]
		IRS NUMBER:				370602744
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		100 NE ADAMS ST
		CITY:			PEORIA
		STATE:			IL
		ZIP:			61629
		BUSINESS PHONE:		3096751000

	MAIL ADDRESS:	
		STREET 1:		100 NE ADAMS ST
		CITY:			PEORIA
		STATE:			IL
		ZIP:			61629

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	CATERPILLAR TRACTOR CO
		DATE OF NAME CHANGE:	19860623
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2011-03-03</periodOfReport>

    <issuer>
        <issuerCik>0000018230</issuerCik>
        <issuerName>CATERPILLAR INC</issuerName>
        <issuerTradingSymbol>CAT</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001171797</rptOwnerCik>
            <rptOwnerName>OSBORN WILLIAM A</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>50 SOUTH LASALLE STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CHICAGO</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60675</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common</value>
            </securityTitle>
            <transactionDate>
                <value>2011-03-03</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1606</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>36331</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Restricted Stock Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F2"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2011-03-03</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1606</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2011-03-03</value>
            </exerciseDate>
            <expirationDate>
                <value>2011-03-03</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>1606</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">This amount includes 225 shares in dividend reinvestment.</footnote>
        <footnote id="F2">Each restricted stock unit represents the equivalent of one share of Caterpillar common stock.  On March 3, 2011, the reporting person's restricted stock units were settled for an equal number of shares of Caterpillar common stock.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>William A. Osborn; L.J. Huxtable, POA</signatureName>
        <signatureDate>2011-03-04</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
